An antiserum was described during the previous tenure of this grant which could recognize Interleukin-1 (IL-1) receptors on mouse lymphoid cells. The antiserum has now been used successfully to immunoprecipitate complexes of IL-1 receptors radiolabeled with 125I-ligand. We have also used the antiserum to create a selected cDNA library. We propose here to identify the cDNA that encodes the IL-1 receptor. The IL-1 receptor cDNA will be sequenced and used as a probe to study IL-1 recptor expression in a variety of cell types. We will also use anti-IL-1 receptor antibodies to investigate the role of IL-1 in the activation and proliferation of T cell clones. The value and significance of these studies relates to the fact that IL-1 serves as an important initiation signal for so many biological systems. IL-1 cannot itself distinguish between an invasive signal versus a signal that results in autoimmune reactions, yet, IL-1 serves as a primary signal in the induction and effector phases of immune and inflammatory reactions. A greater understanding of the nature of the IL-1 receptor molecule itself as well as the signals it transmits should enable one to find appropriate reagents that might control a deleterious reaction as seen in rheumatoid arthritis, autoimmune diseases, and transplantation rejection. Alternatively, one may be able to find alternate means to signal IL-1 receptors in immune deficiency states such that helper T cell responses could be initiated.